Helen Nguyen

Dept. of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign

Title: Adsorption Kinetics of Cryprosporidium Parvum oocysts to Natural Organic Matter: Microscopic Evidence for Secondary Minimum Deposition.

Friday November 7th, 1:30pm, Mann Hall 323

Abstract: Cryptosporidium Parvum is a protozoan pathogen capable of infecting a wide range of mammals including human. Infected animal or human suffer from cryptosporidiosis, a severe diarrheal disease, which lasts 1 to 2 weeks for immunocompetent individuals but could be fatal for infants and immunosuppressed people. Because cryptosporidium oocysts are very resistant to water treatment process including chlorine-based disinfectant, outbreaks of cryptosporidiosis, occur throughout the year. Attachment of C. parvum oocysts to silica or sand surfaces has been studied extensively at scales ranging from nanometer to laboratory bench to field scale. Limited studies suggest that the biofilm and natural organic matter have a significant impact on attachment and transport of C. parvum oocysts in aquatic environment. The objective of this study is to investigate the mechanisms of C. parvum oocyst attachment to natural organic matter. A radial stagnation point flow system combined with a microscope was used to determine the deposition rates of C. parvum oocysts on bare silica surface and silica surface coated with positively charged poly-L-lysine (PLL) or negatively-charged Suwannee River natural organic matter (SRNOM) in solutions with different ionic strengths. Under attractive interaction conditions, oocyst deposition rates on silica surface coated with PLL decreased with ionic strengths. Under repulsive interaction conditions, oocyst deposition rates on silica surface coated with SRNOM increased with salt concentration and became stabilized at the critical deposition concentration (CDC) between 10-20mM. Microscopic evidence of oocyst entrapped in the secondary energy minimum is presented for oocyst deposition on bare silica surface and silica surface coated with SRNOM. Among the entrapped oocysts, some were swept away by the radial flow and some were able to deposit on either bare silica surface or silica surface coated with SRNOM. The absence of deposited oocysts release when washed with 1 mM NaCl suggests that oocyst may deposit in the secondary energy minimum but then transited to deep primary minimum. The experimental data obtained in this study suggest that electrostatic interaction is not the only mechanism that control C. parvum oocyst attachment to natural organic matter.

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